The invention relates to fabric specifications combining fibers of different modulus with particular fabrication techniques to produce reinforcement fabrics of compound modulus characteristics.
Definitions:
Fiber: unit of matter, either natural or manufactured, that forms the basic element of fabrics or textile structures. The fiber is characterized as having a length of at least 100 times its diameter or width.
Fibrous web: a unit of material in web form containing fiber components such as a woven fabric, knit fabric, laid-yarn products and spun bonded products.
Composite fiber: fiber composed of more than one polymer/fiber type, combined by ply-twisting, entangling or other means.
Intimate blend fiber: a technique of mixing two or more dissimilar staple fibers in a very uniform mixture. Usually the stock is mixed before or at the picker.
Crimp: the difference in distance between two points on a fiber in a fabric and the same two points on the fiber after it has been removed from the fabric and straightened under a specified tension, expressed as a percentage of the distance between the two points as it lies in the fabric; may be imparted to the yarn by several yarn processing methods including twisting, texturizing, knit-deknit, stuffer box method, and yarn entangling; may be imparted to the yarn several fabric formation processes such as weaving, knitting, braiding, etc.
Modulus: the ratio of the change in stress or force per unit length to the change in strain expressed as a fraction of the original length or percentage elongation, after crimp has been removed.
Fiber modulus: modulus of fiber.
Fabric modulus: modulus of fabric along test axis (warp/fill/bias) after crimp is removed.
Fabric crimp modulus: modulus of a fabric while crimp is being removed from the fibers as the fabric is loaded; initial part of modulus curve before fibers are under axial tension; significantly lower modulus than fiber/fabric modulus.
Low load elongation (LLE): elongation range over which fabric crimp modulus is measured; typically elongation value is based on a load limit less than 5 pounds per lineal inch (5 pli).
Shrinkagexe2x80x94change in fiber length due to a process mechanism such as dry heat, steam heat or chemistry.
Shrinkage tensionxe2x80x94tension fiber/fabric exerts in fiber axis while shrinkage is performed.
Shrinkage crimpxe2x80x94amount of crimp imparted in the fabric/fiber as a result of shrinkage.
Differential shrinkagexe2x80x94difference in shrinkage between process fiber and reinforcement fiber.
Composite fabricxe2x80x94woven, braided or knitted substrate comprised of more than one fiber type.
Modulus is a characteristic of a material representing how much load (stress) is required to achieve a certain level of stretch (strain). As a result, a low modulus material requires less force than a high modulus material to achieve a given amount of elongation.
The modulus of a material may be constant in a material throughout a range of elongation values or quite variable, particularly for elastomeric composites. Homogeneous, non-reinforced elastomeric materials are generally considered low modulus and are also isotropic, or have the same properties in all directions. Textile fibers are medium or high modulus materials relative to elastomers and are not isotropic but rather have very different properties in the thread line direction vs. the transverse direction of the fiber.
Knit textiles are typically low modulus structures in that they stretch easily and have very high elongation to break. As a result of the knit structure, however, they tend to be inefficient materials on a strength/weight basis and may not always provide reasonable limits of elongation desired for certain component applications such as high pressure hoses and diaphragms.
Woven textile fabrics are typically lower stretch materials and have a modulus that is dependent on the angle of load relative to the orientation of the fabric and fiber. The modulus of the fabric will range from slightly lower than the fiber modulus in the thread-line direction to a much lower modulus at a 45xc2x0 bias angle. The lower modulus on the bias angle is attributed to the ability of the fibers in the fabric to re-orient as load is applied.
The fabric modulus in the bias direction is typically much lower than the fabric modulus along the thread-line. Typical hose and diaphragm reinforcement fabrics have a thread-line modulus of 100-500 pli (0.9%-5.0% elongation @ 5 pli). Alternatively, the bias modulus of these same fabrics (@ 45xc2x0) is reduced to  less than 16-25 pli (20-30% @ 5 pli).
Referring to prior art FIG. 1, there is shown a graph comparing the moduli of standard reinforcement fabric in the fill (1) direction versus 45 degree bias (2) direction. At a given elongation, the fill (weft) oriented material exhibits a higher load due to relatively high fiber stiffness and low weaving crimp. The bias oriented material exhibits a lower load elongation based on combination of warp and fill (weft) crimp as well as the fiber rotation. The low load elongation characteristics are utilized to enhance fabric processing and product characteristics.
Fabric reinforced elastomeric composites have modulus properties greater than the fabric but are still variable in direction due to the nature of the fabric reinforcement. Often, fabric orientation is controlled in the manufacture of fiber reinforced elastomer composites to achieve specific characteristics in the composite product in one or more directions.
Examples of fabric reinforced elastomer composites include hoses, belts, diaphragms and tires. In each of these applications, greater low load elongation is required in the manufacture of these parts than is available in the fabric along the threadline of the fiber. A common solution is to cut the fabric at a bias angle (e.g. 45xc2x0) and orient the fabric in the manufacturing process in the lower modulus direction to aid in the formation, assembly or performance of the composite product.
The bias modulus of 16-25 pli is adequate for many reinforced rubber and elastomer products. However, there remain problems with the prior art. The cost and productivity impact of utilizing fabrics at a bias angle, are non-trivial. Bias cutting the fabric requires special equipment, extra labor and increases waste costs of the process. Similar issues exist in apparel, glove and footwear manufacture.
What is needed is a fabric design which provides a lower fabric crimp modulus to deliver low load elongation in the thread-line direction greater than the 5% upper limit inherent in standard fabrics.
The invention encompasses a fabric system and manufacturing method that allows woven fabric to achieve a lower fabric crimp modulus (higher elongation) in the thread-line direction. The fabric system and method utilizes processing yarns of higher shrinkage than the product reinforcing yarns. The processing yarns are woven together with the reinforcing yarns in various patterns and combinations dependent on the desired fabric characteristics. The fabric is subsequently processed thermally to enable crimp to be imparted into the reinforcing yarns by the differential shrinkage of the processing yarns. By adjusting the ratio of reinforcing yarns to processing yarns, a unique set of characteristics in the fabric can be created, specifically lower modulus/higher initial elongation in the threadline direction of the reinforcing yarn.
These characteristics can be referred to as a compound fabric modulus, and the web or fabric referred to as a bi-modulus fabric; where there is a beneficially lower first modules low load elongation characteristic coupled with a beneficially higher second modules fabric stress limit, a combination not otherwise attainable along a threadline.
It is therefore among the objects of the invention to provide a product and a method for making the product from two different yarn types; where the product is a fibrous web, fabric, fabric-reinforced elastomeric product or part, component, or related article that benefits from having a compound fabric modulus along at least one thread line of the fabric weave. The feature in the fabric may be of benefit in the manufacture and/or the performance of the fabric, component or part.